Electrical stimulation of the brain is an increasingly important approach for treatment of disorders such as Parkinson's disease, essential tremor and dystonia, and for relief of chronic pain. This method can also be used to treat a wide array of neuropsychiatric problems, such as depression, epilepsy, obsessive compulsive disorder or obesity. In general, such stimulation devices interact with the brain by delivering current through an implanted probe in order to modulate brain activity. A typical electrical brain stimulation system comprises a pulse generator operatively connected to the probe via an electrical lead at the distal end. Further, the lead has a connector assembly at the proximal end designed to connect to the pulse generator. Electrical signals are transmitted through the lead to the probe or electrode and thus the desired site in the patient's brain. Normally, access to the desired site in the brain is accomplished by drilling a hole in the patient's skull or cranium using a cranial drill, also called a burr.
As a part of the implant procedure, the probe or electrode must be stabilized in the brain. However, direct attachment of electrical and chemical probes to the brain tissue is impractical. A more easily implementable solution is a system of flexible probes that bend and float with the brain as the brain moves within the cranial cavity. Such probes are secured to the cranium. In this manner, mechanical forces from the outside of the cranium are prevented from acting on the brain-to-probe interface.
In a typical surgical procedure to implant a neurostimulation system for DBS (“Deep Brain Stimulation”), the surgical procedure begins with placing a stereotactic headframe around the patient's head to keep the head stationary. The stereotactic frame also helps the surgeon in the placement of the lead used for the stimulation. Thereafter, the surgeon obtains images of the brain using imaging equipment such as computed tomography (CT) or magnetic resonance imaging (MRI) to map the brain and localize a target site within the brain. In order to provide access to the brain, the surgeon drills a burr hole into the patient's skull. Then, the surgeon inserts a temporary recording stimulation lead into the target site of the brain to test the stimulation, for example, to maximize symptom suppression and minimize side effects before placement of a permanent stimulation electrode lead. When the exact target site of the brain has been determined by the surgeon, the temporary stimulation lead is removed and the surgeon commences the process of inserting the permanent stimulation electrode lead. Using the stereotactic frame and a drive unit, the stimulation electrode lead is inserted through the burr hole in the patient's skull and implanted in the target site within the brain. Once the lead is positioned and tested to determine that the results of stimulation are satisfactory, it is critical that it is not moved. A movement as little as one millimeter of electrode displacement may cause unsatisfactory results or even injury to the brain. Traction on the portion of the lead positioned outside the cranium may cause movement on the portion of the lead positioned within the brain. As understood, it is crucial to achieve a firm and reliable anchoring of the lead in the burr hole. Accordingly, great efforts have been made to obtain reliable means for securing a lead within the burr hole.
For example, in U.S. Pat. No. 4,328,813 a system for anchoring a brain lead within a cranial burr hole is disclosed. The system includes an annular socket having a lead passage and being designed to engage with the burr hole. A plug is arranged to cooperate with the socket and lead passage to secure the lead within the passage and between the plug and socket. However, engagement of the socket and plug according to U.S. Pat. No. 4,328,813 may cause dislodgement of the lead or may pull the lead, which as mentioned above can cause serious problems.
Furthermore, in U.S. Pat. No. 5,464,446 a lead anchoring system is disclosed. The lead anchoring system includes a plug having a central passage, a cap configured to fit the over the plug to seal the burr hole and fixate the lead. A groove is provided in the plug to allow for a suture to be wrapped around the plug to secure the lead in a lead passage of the plug. Thus, the procedure of securing the lead by winding the suture in the groove and attaching the suture may be cumbersome for the surgeon.
In U.S. Pat. No. 5,865,842 a connector system for anchoring a lead or catheter in a cranial burr hole is disclosed. The system includes a base plate, with an adaptor for adapting to a burr hole size, and two element fixation subassembly positioned within the base plate for enabling fixation of the lead to the plate after positioning of the lead with the stereotactic instrument. The fixation subassembly includes a compression seal of compressible material and a compression screw. This construction is mechanically complicated, which may render it expensive to manufacture. Further, it requires a wrench or tool to screw the compression screw into proper position.
A further approach is presented in WO 2008/119041 where an apparatus for securing an implantable lead within tissue, for example, the brain of a patient by fixating the apparatus to the skull of the patient using screws. In particular, the apparatus includes a base adapted to be secured to the patient's skull adjacent a craniotomy using screws, which are screwed into the skull of the patient. This approach thus requires further incisions and holes in the tissue and skull in addition to the burr hole for the implanted stimulation lead.
Hence, there is a need within the art for an improved system and device for firmly securing a medical lead, such as a stimulation lead, in burr hole in a reliable manner. Further, it is important that the lead can be firmly secured without risking any damage on the lead during the securing procedure or during its use.